Ink compositions with excellent light resistance

ABSTRACT

An object of the present invention is to provide ink compositions possessing excellent lightfastness. The cyan ink composition according to the present invention comprises, as colorants, a cyan colorant selected from the group consisting of C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:4, and a mixture of the cyan colorants, and a yellow colorant having a higher fading rate than the cyan colorant. The magenta ink composition according to the present invention comprises, as colorants, a magenta colorant selected from the group consisting of C.I. Pigment Red 122, C.I. Pigment Red 202, C.I. Pigment Red 209, and mixtures of the magenta colorants, and a yellow colorant having a higher fading rate than the magenta colorant.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a cyan ink composition and amagenta ink composition each possessing excellent lightfastness.

[0003] 2. Background Art

[0004] Ink jet recording printers are becoming widely spread in recentyears. Ink jet recording is a printing method wherein droplets of an inkcomposition are ejected and deposited on recording media, such as paper,to perform printing. The feature of the ink jet recording is that imageshaving a combination of high resolution with high quality can be printedat a high speed by means of a relatively inexpensive apparatus. Inparticular, color ink jet recording apparatuses can improve imagequality, can also be utilized as an output device for photographs, andhave also become used, for example, as digital printing machines,plotters, and CAD output devices. The images printed by ink jetrecording printers, which have become widely utilized in this way, areconsidered utilizable in various forms. In particular, for example,photograph-like prints are considered to be placed for display in aplace exposed to light emitted from a fluorescent lamp or directsunlight, for example, in the open for a long period of time. Therefore,lightfastness is a very important property requirement to be satisfiedby records produced by ink jet recording.

[0005] In recent years, inks using a pigment as a colorant have becomeused for improving the lightfastness of records produced by ink jetrecording. In the case of color images yielded by pigment-based inkcompositions, fading of images can be suppressed even when exposed tolight emitted from a fluorescent lamp or direct sunlight, for example,in the open for a long period of time. Even in such a case, however, insome cases, the hue of the image undergoes a change, and, consequently,the whole image becomes yellowish. For this reason, an ink compositionhas been desired that can yield images which are less likely to bedeteriorated even after storage for a long period of time, that is,possesses excellent lightfastness.

SUMMARY OF THE INVENTION

[0006] The present inventors have now found that, in a cyan inkcomposition, a yellow colorant having a specific fading rate added inaddition to a general cyan colorant can suppress a change in hue ofprinted ink and, consequently, can improve lightfastness of the yieldedimages. The present inventors have also found that the improvement inlightfastness of images can also be achieved in the same manner in thecase of a magenta ink composition. The present invention has been madebased on such finding.

[0007] Accordingly, it is an object of the present invention to providean ink composition which can realize images possessing excellentlightfastness.

[0008] Thus, according to one aspect of the present invention, there isprovided a cyan ink composition comprising, as colorants, a cyancolorant selected from the group consisting of C.I. Pigment Blue 15:3,C.I. Pigment Blue 15:4, and a mixture of said cyan colorants, and ayellow colorant having a higher fading rate than the cyan colorant.

[0009] According to another aspect of the present invention, there isprovided a magenta ink composition comprising, as colorants, a magentacolorant selected from the group consisting of C.I. Pigment Red 122,C.I. Pigment Red 202, C. I. Pigment Red 209, and mixtures of saidmagenta colorants, and a yellow colorant having a higher fading ratethan the magenta colorant.

[0010] According to a further aspect of the present invention, there isprovided an ink set comprising a yellow ink composition, a magenta inkcomposition, and a cyan ink composition, the cyan ink composition beingthe cyan ink composition according to the present invention, the magentaink composition being the magenta ink composition according to thepresent invention.

[0011] In the ink compositions according to the present invention, inaddition to a colorant commonly added to ink compositions (that is, acyan colorant or a magenta colorant), a yellow colorant having a higherfading rate than the cyan colorant or magenta colorant is added as thecolorant in the ink compositions. It should be noted that the cyancolorant or the magenta colorant contained as the colorant component inthe ink composition, when exposed to outdoor or other environment afterimage formation, gradually undergoes a change in hue and becomesyellowish. On the other hand, the yellow colorant used in the inkcompositions according to the present invention, when exposed to outdooror other environment after image formation, is faded to render theyellowness of the colorant component low as a whole. Therefore, forexample, when an image is formed using a cyan ink composition containinga cyan colorant and a yellow colorant followed by exposure of the imageto outdoor or other environment, the cyan colorant contained in the inkcomposition yellows with the elapse of time while the yellowness of theyellow colorant is lowered. Consequently, it is considered that therecorded image can hold the original hue of the cyan ink composition andcan form images possessing excellent lightfastness. The same is appliedwith respect to the magenta ink composition. The use of a cyan inkcomposition and a magenta ink composition, which have adopted the aboveconstitution, in an ink set can produce images having betterlightfastness. Further, when the yellow colorant to be used in inkcompositions respectively containing a cyan colorant and a magentacolorant is properly selected while taking into consideration thedifference in fading rate between the cyan colorant and the magentacolorant, the lightfastness of images can be further improved.

DETAILED DESCRIPTION OF THE INVENTION

[0012] Ink Compositions

[0013] The ink compositions according to the present invention may beused in recording methods using ink compositions. Recording methodsusing ink compositions include, for example, an ink jet recordingmethod, a recording method using writing utensils, such as pens, andother various printing methods. Preferably, the ink compositionsaccording to the present invention are used in an ink jet recordingmethod.

[0014] Cyan Ink Composition

[0015] The cyan ink composition according to the present inventionbasically comprises, as colorants, a cyan colorant and a yellow coloranthaving a higher fading rate than the cyan colorant. Here the cyancolorant is selected from the group consisting of C.I. Pigment Blue15:3, C.I. Pigment Blue 15:4, and a mixture of the cyan colorants.

[0016] In the present invention, the “fading rate” refers to a rate atwhich, when a record with ink coated thereon is exposed to light emittedfrom a fluorescent lamp or direct sunlight, for example, in the open fora long period of time, the OD value (optical density) of the ink islowered as compared with that before the exposure. In general, thefading rate can be defined by the following equation through theapplication of a predetermined acceleration test.

Fading rate=100×{(OD value before acceleration test)−(OD value afteracceleration test)}/OD value before acceleration test

[0017] “Yellow colorant having a higher fading rate” refers to a yellowcolorant which is more likely to fade than the cyan colorant accordingto the present invention.

[0018] Specifically, “that the fading rate of the yellow colorant ishigher than the fading rate of the cyan colorant” means that,preferably, the fading rate value of the yellow colorant in apredetermined acceleration test for a predetermined period of time (forexample, 200 hr) is three times or higher than the fading rate value ofthe cyan colorant, more preferably the fading rate value of the yellowcolorant is 5 times or higher than the fading rate value of the cyancolorant.

[0019] Alternatively, “that the fading rate of the yellow colorant ishigher than the fading rate of the cyan colorant” means that, when aprint with a colorant coated thereon is placed under such environmentalconditions as to cause fading, preferably under predeterminedacceleration test conditions, the fading time, of the yellow colorant,defined as the time necessary for the OD value of the print to belowered by a given rate is preferably not more than one-third, morepreferably not more than one-fifth, of the fading time of the cyancolorant.

[0020] In the present invention, the “predetermined acceleration test”refers to an acceleration test for evaluating a deterioration in qualityof an image placed under given conditions for a predetermined period oftime, which conditions have been determined by taking into considerationservice conditions, under which the utilization of the print iscontemplated, and a period of time for which the print is placed underthe above service conditions. For example, when the print is placedoutdoors and is exposed to direct sunlight, the predeterminedacceleration test refers to a test in which a deterioration in thequality of an image, when placed outdoors for a predetermined period oftime, is reproduced in a shortened period of time, while, when the printis placed indoors, the predetermined acceleration test refers to a testin which a deterioration in quality of an image, when placed indoors fora predetermined period of time, is reproduced in a shortened period oftime. In general, in the former, light having higher intensity than thelatter is applied, and, when the desired period of time for which theprint is placed is longer, light having higher intensity is exposed fora longer period of time. Further, in the case of an acceleration testfor reproducing a deterioration in the quality of an image, when placedunder special service conditions, such as under high-humidityenvironment, for a desired period of time, the acceleration test refersto an acceleration test in which such special conditions have been takeninto consideration. A specific example of the acceleration test is anacceleration test performed, for example, under the followingconditions, as a test for reproducing, in a shortened period of time, adeterioration in quality of an image under service conditions such thatthe image is allowed to stand for several years in a room having awindow on the south side. That is, accelelation tester: xenonweather-o-meter Ci35A, manufactured by ATLAS; light source: xenon lamp;optical filter: borosilicate glass; irradiation energy: 0.35 W/m² (340nm); black panel temperature: 63° C.; internal temperature of tester:24° C.; and internal humidity of tester: 60%. These conditions may beproperly varied depending upon expected service conditions. For example,an acceleration test may be carried out using a fluorescent lamp of1,000 to 100,000 luxes according to the expected service conditions.

[0021] Here “yellow OD value” is an OD value as measured for yellowwhich has been printed by blotted image printing (100% duty blottedimage printing) on the so-called “plain paper,” for example, with aMacbeth PCM-II tester manufactured by Macbeth.

[0022] The yellow colorant used in the cyan ink composition according tothe present invention may be any yellow colorant so far as the yellowcolorant has a higher fading rate than the cyan colorant. Therefore, anyof dyes and pigments may be used as the yellow colorant. However, theuse of dyes is preferred.

[0023] Various dyes, for example, direct dyes, acid dyes, foodstuffdyes, basic dyes, reactive dyes, disperse dyes, vat dyes, soluble vatdyes, and reactive disperse dyes, may be used as the dye.

[0024] Any of inorganic and organic pigments may be used as the pigment.Inorganic pigments include, in addition to titanium oxide and ironoxide, carbon blacks produced by known processes, such as contact,furnace, and thermal processes. Organic pigments usable herein includeazo pigments (including azo lake, insoluble azo pigment, condensed azopigment, and chelate azo pigment), polycyclic pigments (for example,phthalocyanine, perylene, perinone, anthraquinone, quinacridone,dioxazine, thioindigo, isoindolinone, and quinophthalone pigments),dye-type chelate pigments (for example, basic dye-type chelate pigmentsand acid dye-type chelate pigments), nitro pigments, nitroso pigments,and aniline black.

[0025] According to a preferred embodiment of the present invention, thepigment is added, to the ink composition, as a pigment dispersionprepared by dispersing the pigment in an aqueous medium with the aid ofa dispersant or a surfactant. Preferred dispersants include dispersantscommonly used in the preparation of pigment dispersions, for example,polymeric dispersants. It would be apparent to a person having ordinaryskill in the art that the dispersant and the surfactant contained in thepigment dispersion would function also as a dispersant and a surfactantfor the ink composition.

[0026] Specific examples of yellow colorants, which are preferred in thepresent invention, include: dyes, such as. C.I. Acid Yellow 23, C.I.Direct Yellow 86, and C.I. Direct Yellow 132; and pigments, such as C.I.Pigment Yellow 13, C.I. Pigment Yellow 17, C.I. Pigment Yellow 74, C.I.Pigment Yellow 83, and C.I. Pigment Yellow 93. The yellow colorant ismore preferably C.I. Acid Yellow 23, C.I. Direct Yellow 86, or C.I.Direct Yellow 132. In the present invention, these yellow colorants maybe used solely or in combination of two or more.

[0027] The amount of the cyan colorant in the cyan ink composition addedin the present invention is preferably about 0.1 to 15% by weight, morepreferably about 0.3 to 4% by weight.

[0028] Further, the amount of the yellow colorant used in the cyan inkcomposition according to the present invention may be properly selectedso far as desired lightfastness can be held. Preferably, however, theamount of the yellow colorant added is 0.005 to 0.05% by weight, morepreferably 0.005 to 0.02% by weight, based on the cyan colorant (1% byweight).

[0029] Magenta Ink Composition

[0030] The magenta ink composition according to the present inventionbasically contains, as colorants, a magenta colorant and a yellowcolorant having a higher fading rate than the magenta colorant. Here themagenta colorant is selected from the group consisting of C.I. PigmentRed 122, C.I. Pigment Red 202, C.I. Pigment Red 209, and mixtures of themagenta colorants.

[0031] In the present invention, the “fading rate” and the“predetermined acceleration test” are as described above.

[0032] Further, the “yellow colorant having a higher fading rate” usedherein refers to a colorant which is more likely to fade than themagenta colorant.

[0033] Specifically, “that the fading rate of the yellow colorant ishigher than the fading rate of the magenta colorant” means that,preferably, the fading rate value of the yellow colorant in apredetermined acceleration test for a predetermined period of time (forexample, 200 hr) is three times or higher than the fading rate value ofthe magenta colorant, more preferably, the fading rate value of theyellow colorant is 5 times or higher than the fading rate value of themagenta colorant.

[0034] Alternatively, “that the fading rate of the yellow colorant ishigher than the fading rate of the magenta colorant” means that, when aprint with a colorant coated thereon is placed under such environmentalconditions as to cause fading, preferably under predeterminedacceleration test conditions, the fading time, of the yellow colorant,defined as the time necessary for the OD value of the print to belowered by a given rate is preferably not more than one-third, morepreferably not more than one-fifth, of the fading time of the magentacolorant.

[0035] The yellow colorant used in the magenta ink composition accordingto the present invention may be selected from those described above inconnection with the yellow colorant used in the cyan ink composition.

[0036] The amount of the magenta colorant in the magenta ink compositionadded in the present invention is preferably about 0.1 to 15% by weight,more preferably about 0.5 to 5% by weight.

[0037] Further, the amount of the yellow colorant used in the magentaink composition according to the present invention may be properlyselected so far as desired lightfastness can be held. Preferably,however, the amount of the yellow colorant added is 0.005 to 0.05% byweight, more preferably 0.007 to 0.03% by weight, based on the magentacolorant (1% by weight).

[0038] In general, magenta ink is more likely to undergo a change in huethan cyan ink. Therefore, when the cyan ink composition and the magentaink composition are used in combination in an ink set, preferably, theyellow colorant used in the magenta ink composition has a higher fadingrate than, that is, is more likely to fade than, the yellow colorantused in the cyan ink composition.

[0039] Other Ink Compositions

[0040] According to another aspect of the present invention, there isprovided an ink set comprising a yellow ink composition, a magenta inkcomposition, and a cyan ink composition. In this case, the cyan inkcomposition is the cyan ink composition according to the presentinvention, or alternatively, the magenta ink composition is the magentaink composition according to the present invention. Further, both thecyan ink composition and the magenta ink composition in the ink set maybe respectively the cyan ink composition according to the presentinvention and the magenta ink composition according to the presentinvention.

[0041] The yellow colorant contained in the yellow ink composition usedin the ink set according to the present invention may be any yellowcolorant so far as yellow can be printed. In the present invention, ayellow pigment is preferred.

[0042] Further, in the present invention, the ink set comprising theyellow ink composition, the magenta ink composition, and the cyan inkcomposition may further comprise a black ink composition. The colorantcontained in the black ink composition usable in the present inventionmay be any colorant so far as black can be printed. In the presentinvention, the use of a black pigment is preferred.

[0043] In the present invention, pigments usable in the yellow inkcomposition and the black ink composition include inorganic pigments andorganic pigments. Inorganic pigments include, in addition to titaniumoxide and iron oxide, carbon blacks produced by known processes, such ascontact, furnace, and thermal processes. Organic pigments usable hereininclude azo pigments (including azo lake, insoluble azo pigment,condensed azo pigment, and chelate azo pigment), polycyclic pigments(for example, phthalocyanine, perylene, perinone, anthraquinone,quinacridone, dioxazine, thioindigo, isoindolinone, and quinophthalonepigments), dye-type chelate pigments (for example, basic dye-typechelate pigments and acid dye-type chelate pigments), nitro pigments,nitroso pigments, and aniline black.

[0044] According to a preferred embodiment of the present invention, thepigment is added, to the ink composition, as a pigment dispersionprepared by dispersing the pigment in an aqueous medium with the aid ofa dispersant or a surfactant. Preferred dispersants include dispersantscommonly used in the preparation of pigment dispersions, for example,polymeric dispersants. It would be apparent to a person having ordinaryskill in the art that the dispersant and the surfactant contained in thepigment dispersion would function also as a dispersant and a surfactantfor the ink composition.

[0045] According to the present invention, the colorant used in theyellow ink composition or the black ink composition may be a single typecolorant or a mixture of a plurality of types of colorants.

[0046] In the ink set according to the present invention, the content ofthe colorant in the yellow ink composition is not particularly limited.The colorant content, however, is preferably 2 to 15% by weight, morepreferably 3 to 5% by weight, based on the yellow ink composition.

[0047] Further, in the present invention, the content of the colorant inthe black ink composition is not particularly limited. The content ofthe colorant in the black ink composition, however, is preferably 2 to15% by weight, more preferably 2 to 8% by weight.

[0048] Water, Water-soluble Organic Solvent, and Other OptionalIngredients

[0049] According to a preferred embodiment of the present invention,when the colorant used in these ink compositions is a pigment, thispigment is preferably added, to the ink composition, as a pigmentdispersion prepared by dispersing the pigment in an aqueous medium withthe aid of a dispersant or a surfactant. Preferred dispersants includedispersants commonly used in the preparation of pigment dispersions, forexample, polymeric dispersants.

[0050] Examples of preferred dispersants include cationic dispersants,anionic dispersants, and nonionic dispersants. Examples of anionicdispersants include polyacrylic acid, polymethacrylic acid, acrylicacid/acrylonitrile copolymer, vinyl acetate/acrylic ester copolymer,acrylic acid/acrylic alkyl ester copolymer, styrene/acrylic acidcopolymer, styrene/methacrylic acid copolymer, styrene/acrylicacid/acrylic alkyl ester copolymer, styrene/methacrylic acid/acrylicalkyl ester copolymer, styrene/α-methylstyrene/acrylic acid copolymer,styrene/α-methylstyrene/acrylic acid/acrylic alkyl ester copolymer,styrene/maleic acid copolymer, vinylnaphthalene/maleic acid copolymer,vinyl acetate/ethylene copolymer, vinyl acetate/fatty acid vinylethylenecopolymer, vinyl acetate/maleic ester copolymer, vinyl acetate/crotonicacid copolymer, and vinyl acetate/acrylic acid copolymer. Examples ofanionic surfactants include sodium dodecylbenzenesulfonate, sodiumlaurylate, and ammonium salt of polyoxyethylene alkyl ether sulfates.Examples of nonionic surfactants include polyoxyethylene alkyl ethers,polyoxyethylene alkyl esters, polyoxyethylene sorbitan fatty acidesters, polyoxyethylene alkylphenyl ethers, polyoxyethylenealkylamines,and polyoxyethylene-alkylamides. They may be used alone or in acombination of two or more. According to a preferred embodiment of thepresent invention, a water-soluble styrene-(meth)acrylic acid resin isutilized as a dispersant. In the ink compositions according to thepresent invention, water or a mixed solution composed of water and awater-soluble organic solvent is suitable as a main solvent. Water maybe pure water obtained by ion exchange, ultrafiltration, reverseosmosis, distillation or the like, or ultrapure water. Further, water,which has been sterilized, for example, by ultraviolet irradiation or byaddition of hydrogen peroxide, is preferred because, when the inkcomposition is stored for a long period of time, it can prevent thegrowth of mold and bacteria.

[0051] Examples of water-soluble organic solvents include high-boilingorganic solvents. High-boiling organic solvents function to prevent theink composition from drying and consequently to prevent head clogging.Examples of preferred high-boiling organic solvents include: polyhydricalcohols, such as ethylene glycol, diethylene glycol, triethyleneglycol, polyethylene glycol, polypropylene glycol, propylene glycol,butylene glycol, 1,2,6-hexanetriol, thioglycol, hexylene glycol,glycerin, trimethylolethane, and trimethylolpropane; alkyl ethers ofpolyhydric alcohols, such as ethylene glycol monoethyl ether, ethyleneglycol monobutyl ether, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether, diethylene glycol monobutyl ether, triethyleneglycol monomethyl ether, triethylene glycol monoethyl ether, andtriethylene glycol monobutyl ether; urea; 2-pyrrolidone andN-methyl-2-pyrrolidone; 1,3-di-methyl-2-imidazolidinone; andtriethanolamine. The amount of the high-boiling organic solvent added isnot particularly limited. The amount of the high-boiling organic solventadded, however, is preferably about 0.5 to 40% by weight, morepreferably about 2 to 20% by weight.

[0052] Further, the ink compositions may contain a low-boiling organicsolvent as the water-soluble organic solvent. Examples of preferredlow-boiling organic solvents usable herein include methanol, ethanol,n-propyl alcohol, iso-propyl alcohol, n-butanol, sec-butanol,tert-butanol, iso-butanol, and n-pentanol. Particularly preferred aremonohydric alcohols. The low-boiling organic solvent has the effect ofshortening the drying time of ink.

[0053] According to a preferred embodiment of the present invention, theink compositions may contain a penetrating agent. Penetrating agentsusable herein include various surfactants, such as anionic, cationic,and amphoteric surfactants; alcohols, such as methanol, ethanol, andiso-propyl alcohol; and lower alkyl ethers of polyhydric alcohols, suchas ethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobutyl ether, triethylene glycol monobutyl ether,propylene glycol monobutyl ether, and dipropylene glycol monobutylether. In particular, the utilization of diethylene glycol monobutylether or triethylene glycol monobutyl ether is preferred. Although theamount of the penetrating agent added may be properly determined, theamount of the penetrating agent is preferably about 1 to 20% by weight,more preferably about 1 to 10% by weight.

[0054] Further, acetylene glycols represented by formula (a) may bementioned as examples of the penetrating agent.

[0055] wherein 0≦m+n≦50; and R¹*, R²*, R³*, and R⁴* each independentlyrepresent an alkyl group, preferably an alkyl group having 1 to 6 carbonatoms.

[0056] Commercially available acetylene glycols may be used as theacetylene glycols represented by the above formula. Specific examplesthereof include OLFINE Y, Surfynol 82, Surfynol 440, Surfynol 465, andSurfynol 485 (all the above products being manufactured by Air Productsand Chemicals Inc.). In particular, the utilization of Surfynol 465 ispreferred. They may be used alone or in combination of two or more. Theamount of the penetrating agent added is preferably 0.1 to 5% by weight,more preferably 0.3 to 3% by weight.

[0057] According to the present invention, the ink composition mayfurther contain a saccharide. Specific examples of preferred saccharidesinclude monosaccharides, disaccharides, oligosaccharides (includingtrisaccharides and tetrasaccharides), and polysaccharides, and preferredexamples thereof include glucose, mannose, fructose, ribose, xylose,arabinose, galactose, aldonic acid, glucitol, sorbit, maltose,cellobiose, lactose, sucrose, trehalose, and maltotriose. Thepolysaccharides refer to saccharides in a wide sense and embracematerials which widely exist in the natural world, such as alginic acid,α-cyclodextrin, and cellulose. Derivatives of these saccharides includereducing sugars of the above saccharides (for example, sugar alcoholsrepresented by the general formula HOCH₂(CHOH)_(n)CH₂OH wherein n is aninteger of 2 to 5), oxidized sugars (for example, aldonic acid anduronic acid), amino acid, and thiosugars. Sugar alcohols areparticularly preferred, and specific examples thereof include maltitoland sorbit.

[0058] The ink compositions according to the present invention mayfurther contain nozzle clogging preventives, preservatives,antioxidants, electric conductivity adjustors, pH adjustors,solubilizers, viscosity modifiers, penetrating accelerators, surfacetension modifiers and the like.

[0059] Examples of preservatives or antimolds include sodium benzoate,pentachlorophenol sodium, 2-pyridinethiol-1-oxide sodium, sodiumsorbate, sodium dehydroacetate, and 1,2-dibenzothiazolin-3-one (ProxelCRL, Proxel BDN, Proxel GXL, Proxel XL-2, and Proxel TN, manufactured byICI).

[0060] Examples of pH adjustors, solubilizers, or antioxidants include:amines, such as diethanolamine, triethanolamine, propanolamine, andmorpholine, and modification products thereof; inorganic salts, such aspotassium hydroxide, sodium hydroxide, and lithium hydroxide; ammoniumhydroxide; quaternary ammonium hydroxides, such as tetramethylammonium;salts of carbonic acid, such as potassium carbonate, sodium carbonate,and lithium carbonate; salts of phosphoric acid, such as potassiumphosphate, sodium phosphate, and lithium phosphate;N-methyl-2-pyrrolidone; urea compounds, such as urea, thiourea, andtetramethylurea; allophanates, such as allophanate and methylallophanate; biurets, such as biuret, dimethylbiuret, andtetramethylbiuret; and L-ascorbic acid and salts thereof.

[0061] The ink compositions according to the present invention mayfurther contain an antioxidant and an ultraviolet absorber, and examplesthereof include: Tinuvin 328, Tinuvin 900, Tinuvin 1130, Tinuvin 384,Tinuvin 292, Tinuvin 123, Tinuvin 144, Tinuvin 622, Tinuvin 770, Tinuvin292, Irgacor 252, Irgacor 153, Irganox 1010, Irganox 1076, Irganox 1035,and Irganox MD 1024, manufactured by Ciba-Geigy; and lanthanide oxides.

[0062] Surface tension modifiers include: alcohols, such asdiethanolamine, triethanolamine, glycerin, and diethylene glycol; andnonionic, cationic, anionic, or amphoteric surfactants.

[0063] Further, in the present invention, a single optional ingredientmay be used as the optional ingredient. Alternatively, a plurality ofoptional ingredients may be selected from an identical group of optionalingredients or a plurality of groups of optional ingredients and used asa mixture.

[0064] In the present invention, the amounts of all the ingredientsconstituting the ink composition are preferably selected so that theviscosity of the ink composition is less than 10 mPa.s at 20° C.

[0065] Recording Method

[0066] The ink compositions according to the present invention are usedin recording methods wherein ink compositions are deposited on recordingmedia to perform printing.

[0067] According to a further aspect of the present invention, there isprovided an ink jet recording method comprising the steps of: ejectingdroplets of the ink composition according to the present invention; anddepositing the droplets onto a recording medium to perform printing.

[0068] Further, according to the present invention, there is alsoprovided a record produced by any one of these recording methods.

EXAMPLES

[0069] The present invention will be described in more detail withreference to the following examples, though it is not limited by theseexamples only. In the following examples, “%” is by weight unlessotherwise specified.

[0070] Examination of Fading Rate of Colorants

[0071] For colorants listed in Table 1, ink compositions were preparedaccording to the following formulations. For each of the inkcompositions thus obtained, a color patch was printed by means of an inkjet printer PM-770C manufactured by Seiko Epson Corp. in such a mannerthat the amount of ink deposited was regulated so as for the OD value ofeach color to be 1.0. Ink composition Colorant 2 wt % Styrene-acrylicacid copolymer (dispersant; only when colorant was pigment) 1 wt %Surfynol 465 1 wt % Glycerin (viscosity modifier) q.s. Pure waterBalance

[0072] The viscosity of each of the ink compositions was modified to 4mPa.s (20° C.).

[0073] The color patches produced for the respective ink compositionswere exposed to light by an acceleration tester under the followingconditions to measure the time (light exposure time) necessary for theOD value of the color patch to be lowered to 0.9 (fading rate 10%).

[0074] Acceleration tester: Xenon weather-o-meter Ci35A, manufactured byATLAS

[0075] Optical filter: Borosilicate glass

[0076] Irradiation energy: 0.35 W/m²

[0077] Black panel temp.: 63° C.

[0078] Internal temp. of tester: 24° C.

[0079] Internal humidity of tester: 60%

[0080] The results were as summarized in Table 1. Colorant Lightexposure time, hr C.I. Pigment Blue 15:3 1,000 C.I. Pigment Blue 15:4950 C.I. Pigment Red 122 1,100 C.I. Pigment Red 202 800 C.I. Pigment Red209 900 C.I. Pigment Yellow 128 850 C.I. Pigment Yellow 13 100 C.I.Pigment Yellow 17 120 C.I. Pigment Yellow 74 300 C.I. Direct Yellow 8650 C.I. Direct Yellow 132 80 C.I. Acid Yellow 23 10

[0081] Preparation of Ink Compositions

[0082] The following ink compositions were prepared by a conventionalmethod. Specifically, the colorants, together with the dispersant, weredispersed. Other ingredients were then added to and mixed with thedispersion. Insolubles having a size larger than a given size wasremoved from the mixture by filtration. Thus, ink compositions wereprepared. The ink compositions thus obtained were combined to prepareink sets.

Example 1 Ink set 1

[0083] Cyan ink composition C.I. Pigment Blue 15:3 2 wt % C.I. PigmentYellow 74 0.01 wt % Styrene-acrylic acid copolymer ½ (dispersant) (ratioto colorant) Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt %Surfynol 465 1 wt % Diethylene glycol (viscosity modifier) q.s. Purewater Balance The viscosity of the ink composition was modified to 5mPa.s (20° C.). Magenta ink composition C.I. Pigment Red 122 3 wt % C.I.Direct Yellow 86 0.03 wt % Styrene-acrylic acid copolymer ½ (dispersant)(ratio to colorant) Glycerin 15 wt % Triethylene glycol monobutyl ether5 wt % Surfynol 465 1 wt % Diethylene glycol (viscosity modifier) q.s.Pure water Balance The viscosity of the ink composition was modified to5 mPa.s (20° C.). Yellow ink composition C.I. Pigment Yellow 128 4 wt %Styrene-acrylic acid copolymer ½ (dispersant) (ratio to colorant)Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt % Surfynol 4651 wt % Diethylene glycol (viscosity modifier) q.s. Pure water BalanceThe viscosity of the ink composition was modified to 5 mpa.s (20° C.).Black ink composition Carbon black 3 wt % Styrene-acrylic acid copolymer½ (dispersant) (ratio to colorant) Glycerin 15 wt % Triethylene glycolmonobutyl ether 5 wt % Surfynol 465 1 wt % Diethylene glycol (viscositymodifier) q.s. Pure water Balance

[0084] 5 mPa.s (20° C.).

Example 2 Ink Set 2

[0085] Cyan ink composition C.I. Pigment Blue 15:3 2 wt % C.I. PigmentYellow 74 0.01 wt % Styrene-acrylic acid copolymer ½ (dispersant) (ratioto colorant) Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt %Surfynol 465 1 wt % Diethylene glycol (viscosity modifier) q.s. Purewater Balance The viscosity of the ink composition was modified to mPa.s(20° C.). Magenta ink composition C.I. Pigment Red 122 3 wt % C.I.Pigment Yellow 13 0.03 wt % Styrene-acrylic acid copolymer ½(dispersant) (ratio to colorant) Glycerin 15 wt % Triethylene glycolmonobutyl ether 5 wt % Surfynol 465 1 wt % Diethylene glycol (viscositymodifier) q.s. Pure water Balance The viscosity of the ink compositionwas modified to mPa.s (20° C.). Yellow ink composition C.I. PigmentYellow 128 4 wt % Styrene-acrylic acid copolymer ½ (dispersant) (ratioto colorant) Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt %Surfynol 465 1 wt % Diethylene glycol (viscosity modifier) q.s. Purewater Balance The viscosity of the ink composition was modified to 5mPa.s (20° C.). Black ink composition Carbon black 3 wt %Styrene-acrylic acid copolymer ½ (dispersant) (ratio to colorant)Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt % Surfynol 4651 wt % Diethylene glycol (viscosity modifier) q.s. Pure water BalanceThe viscosity of the ink composition was modified to 5 mpa.s (20° C.).

Example 3 Ink Set 3

[0086] Cyan ink composition C.I. Pigment Blue 15:3 2 wt % C.I. PigmentYellow 13 0.01 wt % C.I. Pigment Yellow 17 0.01 wt % Styrene-acrylicacid copolymer ½ (dispersant) (ratio to colorant) Glycerin 15 wt %Triethylene glycol monobutyl ether 5 wt % Surfynol 465 1 wt % Diethyleneglycol (viscosity modifier) q.s. Pure water Balance The viscosity of theink composition was modified to mPa.s (20° C.). Magenta ink compositionC.I. Pigment Red 122 3 wt % C.I. Acid Yellow 23 0.2 wt % Styrene-acrylicacid copolymer ½ (dispersant) (ratio to colorant) Glycerin 15 wt %Triethylene glycol monobutyl ether 5 wt % Surfynol 465 1 wt % Diethyleneglycol (viscosity modifier) q.s. Pure water Balance The viscosity of theink composition was modified to mPa.s (20° C.). Light cyan inkcomposition C.I. Pigment Blue 15:3 0.5 wt % C.I. Pigment Yellow 170.0075 wt % Styrene-acrylic acid copolymer ½ (dispersant) (ratio tocolorant) Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt %Surfynol 465 1 wt % Diethylene glycol (viscosity modifier) q.s. Purewater Balance The viscosity of the ink composition was modified to mPa.s(20° C.). Light magenta ink composition C.I. Pigment Red 122 0.5 wt %C.I. Direct Yellow 132 0.025 wt % Styrene-acrylic acid copolymer ½(dispersant) (ratio to colorant) Glycerin 15 wt % Triethylene glycolmonobutyl ether 5 wt % Surfynol 465 1 wt % Diethylene glycol (viscositymodifier) q.s. Pure water Balance The viscosity of the ink compositionwas modified to mPa.s (20° C.). Yellow ink composition C.I. PigmentYellow 128 4 wt % Styrene-acrylic acid copolymer ½ (dispersant) (ratioto colorant) Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt %Surfynol 465 1 wt % Diethylene glycol (viscosity modifier) q.s. Purewater Balance The viscosity of the ink composition was modified to mPa.s(20° C.). Black ink composition Carbon black 3 wt % Styrene-acrylic acidcopolymer ½ (dispersant) (ratio to colorant) Glycerin 15 wt %Triethylene glycol monobutyl ether 5 wt % Surfynol 465 1 wt % Diethyleneglycol (viscosity modifier) q.s. Pure water Balance The viscosity of theink composition was modified to mPa.s (20° C.).

Example 4 Ink Set 4

[0087] Cyan ink composition C.I. Pigment Blue 15:3 2 wt % C.I. PigmentYellow 13 0.01 wt % C.I. Pigment Yellow 17 0.01 wt % Styrene-acrylicacid copolymer ½ (dispersant) (ratio to colorant) Glycerin 15 wt %Triethylene glycol monobutyl ether 5 wt % Surfynol 465 1 wt % Diethyleneglycol (viscosity modifier) q.s. Pure water Balance The viscosity of theink composition was modified to mPa.s (20° C.). Magenta ink compositionC.I. Pigment Red 122 3 wt % C.I. Acid Yellow 23 0.2 wt % Styrene-acrylicacid copolymer ½ (dispersant) (ratio to colorant) Glycerin 15 wt %Triethylene glycol monobutyl ether 5 wt % Surfynol 465 1 wt % Diethyleneglycol (viscosity modifier) q.s. Pure water Balance The viscosity of theink composition was modified to mPa.s (20° C.). Light cyan inkcomposition C.I. Pigment Blue 154 0.5 wt % C.I. Pigment Yellow 17 0.0075wt % Styrene-acrylic acid copolymer ½ (dispersant) (ratio to colorant)Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt % Surfynol 4651 wt % Diethylene glycol (viscosity modifier) q.s. Pure water BalanceThe viscosity of the ink composition was modified to mPa.s (20° C.).Light magenta ink composition C.I. Pigment Red 122 0.4 wt % C.I. PigmentRed 202 0.2 wt % C.I. Direct Yellow 132 0.025 wt % Styrene-acrylic acidcopolymer ½ (dispersant) (ratio to colorant) Glycerin 15 wt %Triethylene glycol monobutyl ether 5 wt % Surfynol 465 1 wt % Diethyleneglycol (viscosity modifier) q.s. Pure water Balance The viscosity of theink composition was modified to mPa.s (20° C.). Yellow ink compositionC.I. Pigment Yellow 128 4 wt % Styrene-acrylic acid copolymer ½(dispersant) (ratio to colorant) Glycerin 15 wt % Triethylene glycolmonobutyl ether 5 wt % Surfynol 465 1 wt % Diethylene glycol (viscositymodifier) q.s. Pure water Balance The viscosity of the ink compositionwas modified to 5 mPa.s (20° C.). Black ink composition Carbon black 3wt % Styrene-acrylic acid copolymer ½ (dispersant) (ratio to colorant)Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt % Surfynol 4651 wt % Diethylene glycol (viscosity modifier) q.s. Pure water BalanceThe viscosity of the ink composition was modified to 5 mPa.s (20° C.).

Example 5 (Comparative) Ink Set 5

[0088] Cyan ink composition C.I. Pigment Blue 15:3 2 wt %Styrene-acrylic acid copolymer ½ (dispersant) (ratio to colorant)Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt % Surfynol 4651 wt % Diethylene glycol (viscosity modifier) q.s. Pure water BalanceThe viscosity of the ink composition was modified to 5 mPa.s (20° C.).Magenta ink composition C.I. Pigment Red 122 3 wt % Styrene-acrylic acidcopolymer ½ (dispersant) (ratio to colorant) Glycerin 15 wt %Triethylene glycol monobutyl ether 5 wt % Surfynol 465 1 wt % Diethyleneglycol (viscosity modifier) q.s. Pure water Balance The viscosity of theink composition was modified to 5 mPa.s (20° C.). Light cyan inkcomposition C.I. Pigment Blue 153 0.5 wt % Styrene-acrylic acidcopolymer ½ (dispersant) (ratio to colorant) Glycerin 15 wt %Triethylene glycol monobutyl ether 5 wt % Surfynol 465 1 wt % Diethyleneglycol (viscosity modifier) q.s. Pure water Balance The viscosity of theink composition was modified to 5 mPa.s (20° C.). Light magenta inkcomposition C.I. Pigment Red 122 0.5 wt % Styrene-acrylic acid copolymer½ (dispersant) (ratio to colorant) Glycerin 15 wt % Triethylene glycolmonobutyl ether 5 wt % Surfynol 465 1 wt % Diethylene glycol (viscositymodifier) q.s. Pure water Balance The viscosity of the ink compositionwas modified to 5 mPa.s (20° C.). Yellow ink composition C.I. PigmentYellow 128 4 wt % Styrene-acrylic acid copolymer ½ (dispersant) (ratioto colorant) Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt %Surfynol 465 1 wt % Diethylene glycol (viscosity modifier) q.s. Purewater Balance The viscosity of the ink composition was modified to 5mPa.s (20° C.). Black ink composition Carbon black 3 wt %Styrene-acrylic acid copolymer ½ (dispersant) (ratio to colorant)Glycerin 15 wt % Triethylene glycol monobutyl ether 5 wt % Surfynol 4651 wt % Diethylene glycol (viscosity modifier) q.s. Pure water BalanceThe viscosity of the ink composition was modified to 5 mPa.s (20° C.).

[0089] Evaluation Test

[0090] Evaluation Test on Lightfastness of Ink Compositions

[0091] The ink sets 1 and 2 were used with an ink jet printer PM-900Cmanufactured by Seiko Epson Corp., and the ink sets 3 and 4 were usedwith an ink jet printer PM-770C manufactured by Seiko Epson Corp. toperform printing under the following conditions.

[0092] Printing paper: gloss film manufactured by Seiko Epson Corp.

[0093] Printing mode: resolution 720 dpi×720 dpi

[0094] Printing pattern: blotted image (100% duty) (printing was carriedout for each ink composition included in the ink set)

[0095] Blotted image prints were exposed under the following conditions.

[0096] Optical filter: Borosilicate glass

[0097] Irradiation energy: 0.35 w/m² (340 nm)

[0098] Black panel temp.: 63° C.

[0099] Internal temp. of tester: 24° C.

[0100] Internal humidity of tester: 60%

[0101] Light exposure: 100 kJ/m² (79 hr)

[0102] For the prints before and after the exposure, the L*a*b* colorsystem of the color difference indication method specified in CIE(Commission International de l'Eclairage) was measured with MacbethCE-7000 spectrophotometer manufactured by Machbeth, and a change in hueΔE was calculated by equation

ΔE=(ΔL ^(*2) +Δa ^(*2) +Δb ^(*2))^(½)

[0103] ΔE values can be evaluated as follows.

[0104] ΔE≦3: good

[0105] 3<ΔE≦5: practically acceptable

[0106] 5<ΔE: practically not acceptable

[0107] The results were as summarized in Table 2.

[0108] Evaluation Test on Lightfastness of Printed Images

[0109] Printing was carried out in the same manner as described above inconnection with the evaluation test on lightfastness of the inkcomposition, except that the following print pattern was printed.

[0110] Printing pattern: portrait image (color image)

[0111] Images thus obtained were allowed to stand indoors at a placeexposed to direct sunlight for one month. The images before and afterthe standing were visually inspected by 50 evaluators to determine thenumber of evaluators who could perceive a change in hue of image betweenbefore and after the standing. The lightfastness of images produced bythe ink sets according to the present invention were evaluated accordingto the following criteria.

[0112] A: Less than 25 evaluators could perceive a change in hue ofimage.

[0113] B: Not less than 25 evaluators could perceive a change in hue ofimage.

[0114] The results were as summarized in Table 2. TABLE 2 Ink Ink InkInk Ink set 1 set 2 set 3 set 4 set 5 ΔE Cyan ink 1.0 0.8 1.2 1.2 5.3Magenta ink 1.8 1.7 2.0 2.0 7.2 Light cyan ink — — 0.5 0.3 3.1 Lightmagenta ink — — 0.7 0.4 4.6 Evaluation of lightfastness A A A A B ofcolor image

1. A cyan ink composition comprising, as colorants, a cyan colorantselected from the group consisting of C.I. Pigment Blue 15:3, C.I.Pigment Blue 15:4, and a mixture of said cyan colorants, and a yellowcolorant having a higher fading rate than the cyan colorant.
 2. The cyanink composition according to claim 1, wherein the content of the yellowcolorant is 0.005 to 0.05% by weight based on the cyan colorant.
 3. Amagenta ink composition comprising, as colorants, a magenta colorantselected from the group consisting of C.I. Pigment Red 122, C.I. PigmentRed 202, C.I. Pigment Red 209, and mixtures of said magenta colorants,and a yellow colorant having a higher fading rate than the magentacolorant.
 4. The magenta ink composition according to claim 3, whereinthe content of the yellow colorant is 0.005 to 0.05% by weight based onthe magenta colorant.
 5. The ink composition according to any one ofclaims 1 to 4, wherein the yellow colorant is a dye.
 6. The inkcomposition according to claim 5, wherein the dye is selected from thegroup consisting of C.I. Acid Yellow 23, C.I. Direct Yellow 86, C.I.Direct Yellow 132, and mixtures of said dyes.
 7. The ink compositionaccording to any one of claims 1 to 6, which is used in an ink jetrecording method.
 8. An ink set comprising a yellow ink composition, amagenta ink composition, and a cyan ink composition, said cyan inkcomposition being the ink composition according to any one of claims 1,2, 5, and
 6. 9. An ink set comprising a yellow ink composition, amagenta ink composition, and a cyan ink composition, said magenta inkcomposition being the ink composition according to any one of claims 3to
 6. 10. An ink set comprising a yellow ink composition, a magenta inkcomposition, and a cyan ink composition, said cyan ink composition beingthe ink composition according to any one of claims 1, 2, 5, and 6, saidmagenta ink composition being the ink composition according to any oneof claims 3 to
 6. 11. The ink set according to any one of claims 8 to10, which further comprises a black ink composition.
 12. The ink setaccording to any one of claims 8 to 11, which is used in an ink jetrecording method.
 13. A recording method comprising the step ofdepositing an ink composition onto a recording medium to performprinting, said ink composition being one according to any one of claims1 to
 6. 14. An ink jet recording method comprising the steps of:ejecting droplets of an ink composition; and depositing the dropletsonto a recording medium to perform printing, said ink composition beingone according to any one of claims 1 to
 6. 15. A record produced by themethod according to claim 13 or 14.